1. Field of the Invention
Embodiments of the present invention generally relate to systems and methods for protecting marine surfaces against biological fouling. More particularly, embodiments relate to systems and methods for reducing biological fouling on vortex-induced vibration reduction devices for offshore hydrocarbon exploration and production.
2. Description of the Related Art
In off-shore operations, vortex-induced vibration or “VIV” is caused by the flow of water around a tubular, such as a riser or other marine element. The flow of water leads to the shedding of vortices which cause alternating forces on either side of the marine element, thereby causing the element to vibrate. When the frequency of the shedding vortices is at or near the natural frequency of the marine element, resonance occurs which can cause potentially destructive levels of vibration that adversely affect the platform structure itself, in addition to the equipment and personnel on the platform.
To counteract VIV, systems to divert or absorb the vibrational energy of the water have been used, such as fairings, strakes, and shrouds. VIV reduction devices generally reduce vortex-induced forces and minimize drag on the riser by reducing or breaking up the low pressure areas that form down-current of the riser. However, marine environments must overcome the additional challenge of biological fouling or “biofouling.”
Biofouling is the undesirable accumulation of microorganisms, plants, algae, and other organisms on marine structures. There are two categories of biofouling: microfouling, which is the formation of biofilms and bacterial adhesion and macrofouling, which is the attachment of larger organisms, such as barnacles, mussels, polychaete worms, bryozoans, and seaweed. This build up of organisms on the surface of marine elements increases the weight and size of the VIV reduction devices, which in turn increases vortex-induced vibrations and drag forces exerted on the fairings. Furthermore, biofouling can prevent a VIV reduction device, such as fairings from rotating or weathervaning about the marine element.
There is a need, therefore, for systems and methods for reducing VIV and drag forces with vortex-induced vibration reduction devices while also reducing or preventing biofouling.